Letter regarding article by Li et al.: Single-bundle versus double-bundle anterior cruciate ligament reconstruction: an up-to-date meta-analysis

Dear Editor,

Recently, we read with great interest the article by Li et al. [1] entitled “Single-bundle versus double-bundle anterior cruciate ligament reconstruction: an up-to-date meta-analysis” published in February 2013 in “International Orthopaedics”. Li et al. performed a meta-analysis to compare the results of arthroscopic single-bundle and double-bundle anterior cruciate ligament (ACL) reconstruction. It is an interesting study. Nevertheless, we have several queries which we would like to communicate with the authors.

1. Five electronic databases (PubMed, Cochrane Library, EMBASE, BIOSIS and Ovid) for randomised controlled trials were systematically searched by the authors. However, the authors did not focus specifically or in any detail on the issue of the completeness of the search strategy report for databases. The search strategy report plays an important role in meta analysis.

2. It is not appropriate that summary odds ratio (OR) and standard mean difference (SMD) estimates with corresponding 95 % CIs were derived by using the method of Mantel-Haenszel (M-H) or inverse variance (IV) with the assumptions of a random-effects model in the forest plots (Figures 3, 5 and 9). Rather, studies should be combined by using the DerSimonian and Laird random-effects model, which consider both within- and between-study variations.

3. The authors clearly stated that “the pooling of data showed that there was no significant difference between the single bundle and double-bundle techniques (OR 1.56; 95 % CI 0.82–2.95; P = 0.18)” in the objective International Knee Documentation Committee (IKDC) results section, which was controversial. We suggest that “no significant difference” should be replaced by “significant difference” in the results section. Meanwhile, the result of the forest plots for objective IKDC showed that the difference was statistically significant between single-bundle and double-bundle techniques.

4. The publication language was limited to English in the meta-analysis. Therefore, the authors should mention the potential importance of language bias in the limitations of their meta-analysis. It is sufficient that publication bias was assessed by visual examination of the funnel plot. Funnel plot symmetry should be further assessed by statistical tests (e.g., Egger’s linear regression test or Begg’s rank correlation test). However, it is not clear that publication bias was assessed for which outcome. Actually, publication bias should be assessed for all the outcomes.

Moreover, further high quality RCTs based on larger sample sizes are still needed to compare the arthroscopic single-bundle and double-bundle ACL reconstruction. We believe that our remarks will contribute to more accurate elaboration of the results presented by Li et al.